Slavery as necessity.
“To greatly simplify, in this vision, what makes the ancient economy distinct from other subsequent forms was its substantial reliance on slavery (as opposed to dependent tenants or wage laborers) as the main system by which labor beyond subsistence was organized, with the elite extracting effectively 100% rents off of the slaves they owned. The enslaved population, it was posited, was mostly generated by warfare and thus warfare was also fundamental to the system. Under this vision, while some free small farmers exist, they primarily work only for subsistence and are minimally engaged in markets, while most of the surplus, including agricultural goods for trade and non-agricultural goods, were produced by slaves”
https://acoup.blog/2024/07/26/collections-teaching-paradox-imperator-part-iia-pops-and-chains/